Pfizer, Moderna Covid-19 vaccines prove to be effective: CDC

A study involving care personnel, first responders and essential workers provides strong evidence that Covid-19 vaccines are highly effective in preventing SARS-CoV-2 infections in real-world conditions.

Centers for Disease Control and Prevention (CDC) said in a statement that the groups mentioned in the study are more likely than the general population to be exposed to the virus due to their occupations.

The study looked at the effectiveness of Pfizer-BioNTech and Moderna mRNA vaccines in preventing SARS-CoV-2 infections among 3,950 study participants in six US states over a 13-week period from 14 December 2020 to 13 March 2021.

Results showed that following the second dose of vaccine (the recommended number of doses), risk of infection was reduced by 90 per cent two or more weeks after vaccination. Following a single dose of either vaccine, the participants’ risk of infection with SARS-CoV-2 was reduced by 80 per cent two or more weeks after vaccination.

It takes about two weeks following each dose of vaccine for the body to produce antibodies that protect against infection. As a result, people are considered ‘partially vaccinated’ two weeks after their first dose of mRNA vaccine and ‘fully vaccinated’ two weeks after their second dose. These new vaccine effectiveness findings are consistent with those from Phase 3 clinical trials conducted with the vaccines before they received Emergency Use Authorizations from the Food and Drug Administration. Those clinical trials evaluated vaccine efficacy against Covid-19 disease, while this study evaluated vaccine effectiveness against infection, including infections that did not result in symptoms.

“This study shows that our national vaccination efforts are working,” said CDC Director, Rochelle Walensky.

“The authorised mRNA COVID-19 vaccines provided early, substantial real-world protection against infection for our nation’s health care personnel, first responders, and other frontline essential workers.

“These findings should offer hope to the millions of Americans receiving Covid-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead. The authorised vaccines are the key tool that will help bring an end to this devastating pandemic.”

One of this study’s strengths is its design: participants self-collected nasal swabs each week for RT-PCR laboratory testing, regardless of whether they had developed symptoms of illness. Researchers were able to look for evidence of SARS-CoV-2 infection irrespective of symptoms. A small number (10.7 per cent) of infections in this study were asymptomatic. However, the majority of infections (58 per cent) occurred among people whose infections were identified by testing before they developed symptoms or knew they were infected. The study demonstrates that these two mRNA vaccines can reduce the risk of all SARS-CoV-2 infections, not just symptomatic infections.

This is important because preventing both asymptomatic and pre-symptomatic infections among health care workers and other essential workers through vaccination can help prevent the spread of SARS-CoV-2 to those they care for or serve. Findings from this study complement earlier reports that these two mRNA COVID-19 vaccines can reduce both asymptomatic and symptomatic SARS-CoV-2 infections.

This study also provided positive news about partial (one-dose) vaccination. The one-dose VE estimate of this study (80 per cent) is consistent with other recent VE studies following the first dose of Pfizer-BioNTech vaccine among health care providers. Studies conducted in the UK and Israel showed that one dose was about 70 per cent and 60 percent effective, respectively, against SARS-CoV-2 infection. The current results provide reassurance that people start to develop protection from the vaccine two weeks after their first dose. The greatest protection was seen among those who had received both recommended doses of the vaccine.

In Australia, people at increased risk of exposure (health, aged care and disability care workforce, aged and disability care residents and people in high risk settings such as quarantine and border workers will be prioritised for vaccination. Priority access will also be given to people working in critical services as well as individuals who have an increased risk of developing a serious illness from Covid-19.

As of 28 March 2021, a total of 541,761 vaccine doses have been administered in Australia.

The Covid-19 vaccine will be voluntary and free for everyone in Australia.

The Federal Government has invested $363 million to support research and development to contribute to the global effort to find successful vaccines and treatments to stop the spread of Covid-19. It has also invested more than $3.3 billion in promising vaccine candidates and current has four separate agreements for the supply of Covid-19 vaccinations if they are proved to be safe and effective.

The Pfizer/BioNTech candidate has been provisionally approved for use in Australia and is the first Covid-19 vaccine to be tested in adolescents.

There are currently nine other vaccine candidates undergoing clinical trial stages including:

  • AstraZeneca / University of Oxford
  • Novavax,
  • Moderna
  • CureVac
  • Sanofi / GSK
  • Inovio
  • Clover Biopharmaceuticals / GSK / Dynavax
  • Institut Pasteur / Merck / Themis
  • University of Hong Kong